A heat sink is a device for the passive dissipation of heat. Heat sinks are typically used with electronic device where the heat dissipation of the basic device is insufficient to maintain the temperature in a desired range. Light emitting diodes (LED), especially those used for indoor and outdoor lighting require a heat sink for optimal operation.
A heat sink can have a significant impact on the operation of an LED. Changes in the junction temperature of an LED can affect the lifetime, and the energy efficiency, of the LED, with lower temperatures extending the lifetime and increasing the energy efficiency. Furthermore, the equilibrium brightness of an LED will also be greater as the junction temperature is decreased, due to the increased efficiency of the LED.
A typical heat sink for an LED, or other electronic device, is designed to maximize surface area in order to maximize the transfer of heat from the electronic device to the surrounding air. Heat is drawn out of the electronic device by conduction into the heat sink. Then the heat sink primarily dissipates heat into the surrounding air by convection. The design of a typical heat sink therefore uses highly heat conductive materials for the body of the heat sink, and maximizes surface area to maximize contact with the surrounding air. Furthermore, the shape of a heat sink will typically include vertically aligned pins, fins or channels, which will allow the warmed air in contact with the heat sink to rise and flow away from the electronic device. Although a heat sink will also dissipate heat by radiation, this factor is often neglected in the design because it is believed that dissipation of heat by radiation at normal temperatures (0 to 100° C.) is generally small in comparison to dissipation of heat by convection.
A molecular fan is a coating which may be applied to a surface, to increase substrate surface emissivity and thus to enhance “active” heat dissipation by radiation. Such coatings are described in U.S. Pat. Nos. 7,931,969 (Lin, Apr. 26, 2011) and 8,545,933 (Lin, Oct. 1, 2013). The molecular fan takes advantage of the high emissivity in the infra-red of discrete molecules (as opposed to extended solids) which result from transitions between different vibrational states. The molecular fan will include nanoparticles to increase surface area, and functionalized nanomaterials to provide the discrete molecules on the surface of the coating that will radiate infra-red light as they transition between different vibrational states. An emulsion that hardens upon curing is also included in a molecular fan coating material, to adhere the nanoparticles and functionalized nanomaterials on the surface of the device or heat sink. The molecular fan coating provides good surface hardness, provides resistance to fingerprints, inhibits corrosion and is easy to clean.
Applying a molecular fan onto the surface of a typical heat sink will increase heat dissipation. However, a typical heat sink is designed to maximize heat dissipation by convection rather than radiation, and includes surfaces which do not radiate away from the device or heat sink, allowing the radiation to be reabsorbed. Therefore, application of a molecular fan onto such surfaces of a typical heat sink does not significantly improve heat dissipation from those surfaces.